Metallic salt deposition on porous particles by dry impregnation in fluidized bed: Effect of drying conditions on metallic nanoparticles distribution

In this paper, the fluidized bed dry impregnation of coarse alumina porous particles by a metallic salt, manganese nitrate, is investigated. In this technique the penetration of each drop of metallic solution in the porous solid particle and solvent evaporation takes place at the same time, then liquid diffusion phenomenon is negligible. So, the metal loading is directly related to the operating time and liquid flow rate and concentration. It is found that the competition between two phenomena, drying and capillary flow, controls the deposit location. In order to determine the importance of the solvent evaporation process compared to the solution penetration by capillarity, an impregnation module, IM, was defined as the ratio between the drying characteristic time and a capillary penetration time. The adequate choice of the operating conditions (bed temperature, liquid and fluidization gas flow rate) allows a uniform deposition of the metallic precursor inside the porous matrix or on the support surface. The impregnation under slow drying conditions (IM ≥ 10 and solvent content in the bed atmosphere τs ≥ 0.2) leads to a homogeneous deposition inside the pores. Under fast drying conditions (IM < 5 and τs < 0.2), the deposit is located at the particle external surface.In the case of slow drying, the impregnation kinetics can be represented by a “shrinking core” model. The critical impregnation rate is controlled by the competition between dissolution and recrystallization at the elementary grain scale. The size of the metal crystallites depends on the pore mean size and size distribution and on the drying rate

Production of a diluted solid tracer by dry co-grinding in a tumbling ball mill

This paper presents a study on the production by co-grinding of a diluted solid tracer, sized less than 10 mm and containing less than 2 wt. % of active product, used in the field of grounds contamination and decontamination. Co-grinding was performed in a tumbling ball mill and permits to produce easily a diluted tracer without implementing several apparatus. The two products were ground separately first and then together. The follow-up of the particles size and morphology, as well as the modelling of the grinding kinetics have permitted to propose a mechanism by which the diluted solid tracer is produced. The influence of the operating conditions (nature and initial size of the diluting medium, ball and powder filling rates, proportion of the polluting tracer) on products grinding was studied. Thus, we have defined optimum co-grinding conditions permitting to produce a tracer offering the required properties. These ones are classical for tumbling ball mills. This kind of mill is very interesting since its sizes can easily be extrapolated to answer to an industrial demand

Synthèse et dépôt de nanoparticules métalliques dans un support poreux par imprégnation en voie sèche dans un lit fluidise : élaboration de catalyseurs supportes

Le travail présenté dans ce manuscrit traite de la synthèse et du dépôt de nanoparticules métalliques dans les grains d'un support poreux par imprégnation en voie sèche en lit fluidisé. Le principe de cette technique consiste en la pulvérisation d'une solution contenant une source de métal dans un lit fluidisé chaud de particules poreuses. Deux types de solutions de précurseurs ont été utilisés : un sel métallique et une suspension colloïdale. L'étude expérimentale est consacrée à l'influence de paramètres liés au procédé et aux propriétés physico-chimiques du support sur la dispersion des éléments métalliques au sein de la matrice ainsi qu'à leur répartition en taille. Les résultats obtenus ont montré que l'efficacité de l'opération est de 100%. Le lieu de dépôt peut être choisi selon les conditions opératoires de l'imprégnation/séchage grâce à un nouveau nombre adimensionnel, le Module d'imprégnation. Un dépôt peut être réalisé à la surface des particules de support ou à l'intérieur des grains lors de la pulvérisation de sels métalliques ainsi que de suspensions colloïdales sur un support de taille pouvant aller de 100 μm à quelques millimètres. Les conditions de calcination présentent un effet, plus ou moins marqué selon la nature du support employé, sur la répartition des éléments métalliques et le paramètre clé est la vitesse de montée en température. La porosité du support joue également un rôle car le diamètre des pores de la matrice fixe la taille maximale des amas de nanoparticules formés. Enfin, les matériaux composites ainsi préparés présentent une activité et une sélectivité intéressantes lors de diverses réactions catalytiques telles que l'hydrogénation de composés aromatiques ou la synthèse de nanotubes de carbone. Leurs performances sont similaires aux catalyseurs élaborés de façon traditionnelle

Model arenes hydrogenation with silica-supported rhodium nanoparticles:The role of the silica grains and of the solvent on catalytic activities

Silica-supported rhodium-based nanoheterogeneous catalysts were easily prepared by impregnation with a pre-stabilized colloidal suspension. The resulting catalysts contain rhodium nanoparticles well-dispersed in the silica pores with a mean size of 5 nm. Influence of the silica grains size and of the solvent was investigated in arenes hydrogenation. It appeared that the size of the silica grains has a minimal influence on the reaction rate but the supported nanocatalysts displayed higher TOFs in hexane than in water

Rhodium colloidal suspension deposition on porous silica particles by dry impregnation: Study of the influence of the reaction conditions on nanoparticles location and dispersion and catalytic reactivity

Rhodium composite nanomaterials were synthesized by an innovating process called dry impregnation in a fluidized bed. It consists in spraying an aqueous colloidal suspension of rhodium on silica porous particles. The use of this precursor solution containing preformed nanoparticles avoids calcination/activation step. Different composite nanomaterials were prepared displaying various metal loadings. The operating conditions were tuned to modify τs, the solvent vapour saturation rate value, in order to influence the deposit location: either uniform on the whole silica particles or at the particles surface like a coating. τs is defined as the ratio between solvent content in the bed atmosphere and the maximum solvent content. The obtained samples were investigated in catalytic hydrogenation of aromatic compounds under very mild conditions. Their catalytic performances were compared to those of the original colloidal suspension in one hand and of a similar catalyst prepared through wet impregnation in another hand. Interesting activity and selectivity were observed.This illustrates the interest of the dry impregnation method: this way allows an easy control of the metal loading as well as of the metal loading location in the support particles. Moreover, the support particle size and morphology are preserved

Optimisation of sludge pretreatment by low frequency sonication under pressure

This work aims at optimizing sludge pretreatment by non-isothermal sonication, varying frequency, US power (P-US) and intensity (I-US varied through probe size), as well as hydrostatic pressure and operation mode (continuous vs. sequential - or pulsed - process). Under non isothermal sonication sludge solubilization results from both ultrasound disintegration and thermal hydrolysis which are conversely depending on temperature. As found in isothermal operation: - For a given specific energy input, higher sludge disintegration is still achieved at higher PUS and lower sonication time. - US effects can be highly improved by applying a convenient pressure. - 12 kHz always performs better than 20 kHz. Nevertheless the optimum pressure depends not only on P-US and I-US, but also on temperature evolution during sonication. Under adiabatic mode, a sequential sonication using 5 min US-on at 360 W, 12 kHz, and 3.25 bar and 30 min US-off gives the best sludge disintegration, while maintaining temperature in a convenient range to prevent US damping

Heterogeneous Fenton oxidation using Fe-ZSM5 catalyst for removal of ibuprofen in wastewater

Heterogeneous Fenton oxidation using Fe-zeolite catalyst (of ZSM5 type) was investigated for the removal of ibuprofen (20 mg/L) in water. In particular, the effects of catalyst concentration, oxidant dosage, temperature, solution pH, and water matrix on pollutant conversion and mineralization were evaluated. The activity of leached iron species in solution was also measured to determine the contribution of the homogeneous reaction. Oxidation rate of ibuprofen obeyed a pseudo-first-order kinetics with respect to the pollutant concentration, and the apparent rate constant increased with catalyst and hydrogen peroxide concentrations in the investigated ranges (1-5 g/L of Fe-zeolite and 0.5-7 times the stoichiometric amount of oxidant). Energy activation of 53 kJ/mol was obtained from Arrhenius plot. However, the mineralization yield was not significantly improved by a too large excess of H2O2 or increase of temperature. In the selected conditions (25 °C, 4.8 g/L of catalyst, 2 times the stoichiometric amount of H2O2), 88% of ibuprofen and 27% of TOC were removed after 3 hours of reaction under “natural” pH conditions. Very low leaching (up to 0.2 mg/L) and negligible activity of leached iron in solution indicated that Fenton reaction was mainly induced by iron species on the catalyst surface. Degradation rate of ibuprofen was slower in wastewater effluent as compared to distilled water, mainly due to alkaline buffering and radical scavenging effects of organic and inorganic compounds present in the matrix. Mono- and multi-hydroxylated ibuprofen adducts were found as main oxidation intermediates -in line with free-radical mechanism- as well as 4-isobutylacetophenone from decarboxylation route

Feasibility of a heterogeneous Fenton membrane reactor containing a Fe-ZSM5 catalyst for pharmaceuticals degradation: Membrane fouling control and long-term stability

Fenton oxidation is one of the promising advanced oxidation processes for the efficient elimination of pharmaceuticals from wastewater. The strong oxidation ability of this process is attributed to the generation of highly reactive hydroxyl radicals (radical dotOH) in the solution. In the present study, heterogeneous micro-sized zeolite catalysts that contain iron have been used in the Fenton-like process. This process enables operation in a wide pH range and facilitates the reuse of catalysts. Indeed, the coupling of the heterogeneous Fenton reaction with membrane filtration will ensure catalyst retention in the effluent compartment during the continuous water treatment. This study then investigated the fouling control strategies and membrane long-term stability in the heterogeneous Fenton reactor. During the filtration of the zeolite catalyst suspension, the critical flux for irreversible fouling was determined. One of the strategies to control membrane fouling can then be to choose an operating flux below this critical flux. In the case where a flux value above the critical flux is chosen, the results demonstrated total efficiency of hydrodynamic backwashing to eliminate hydraulically reversible fouling. Concerning the question of polymeric membrane long-term stability, it has been demonstrated that due to contact with the Fenton medium, membrane material undergoes oxidation and polymeric chain scissions. This latter is strongly linked to the decline in the mechanical resistance of membranes. In the tested conditions, despite the degradation to membrane material, the critical flux for irreversible fouling remained unchanged on aged membranes

Sonolysis and sono-Fenton oxidation for removal of ibuprofen in (waste)water

Two sonochemical processes were compared for the removal of ibuprofen in different water matrixes (distilled water and effluent from wastewater treatment plant). The effect of various operating parameters, such as pH (2.6–8.0), ultrasound power density (25–100 W/L), sonication frequency (12–862 kHz), addition of radical promoters (H2O2 and Fenton’s reagent) or scavengers (n-butanol and acetic acid), was evaluated. Sono-degradation of ibuprofen followed a first-order kinetic trend, whose rate constant increased with ultrasound density and frequency. For this hydrophobic and low volatile molecule, a free-radical mechanism at the bubble interface was established. Coupling ultrasound with Fenton reaction showed a positive synergy, especially in terms of mineralization yield, while adding H2O2 alone had no significant beneficial effect. Dedicated experiments proved this synergy to be due to the enhanced regeneration of ferrous ions by ultrasound. Efficacy of the sonolysis process was hampered in wastewater matrix, mainly as the consequence of higher pH increasing the molecule solubility. However, after convenient acidification, sono-Fenton oxidation results remained almost unchanged, indicating no significant radical scavenging effects from the effluent compounds

Degradation of ibuprofen by photo-based advanced oxidation processes: exploring methods of activation and related reaction routes

Several homogeneous photo-based advanced oxidation processes - namely photolysis, photo- oxidation and photo-Fenton oxidation - were investigated for the elimination of ibuprofen in water. The effects of several operating parameters, such as the lamp type (low or medium pressure mercury, xenon-arc), the concentration of hydrogen peroxide (0.5 to 7 times the stoichiometric amount required for mineralization) and the concentration of Fenton reagent, were quantified. Photo-Fenton oxidation was also combined with low-frequency sonication to investigate possible synergistic interactions. Ibuprofen degradation under ultraviolet photolysis and ultraviolet/hydrogen peroxide oxidation followed pseudo-first-order kinetics with respect to the pollutant concentration and the apparent rate constant increased with lamp power (6-10 W) and oxidant concentration. Photo-Fenton oxidation under ultraviolet light (L1 lamp, 254 nm, 6 W) and visible light (L2 lamp, 360-740 nm, 150 W) led to complete ibuprofen removal after 3 h, but the mineralization yield of the L1/Fenton process (82%) was higher than that of the L2/Fenton process (59%) because of the effects of ultraviolet/hydrogen peroxide oxidation in the former. Coupling L2/Fenton with sonication improved the degradation rate of the molecule at low Fenton reagent concentration, but the beneficial effect of ultrasound on ferrous iron regeneration vanished when the iron to ibuprofen molar ratio was close to 1. An overall reaction scheme for ibuprofen degradation is proposed based on the transformation products detected during these processes